1. Field of the Invention:
The present invention relates to an apparatus for steering the front and rear wheels of a motor vehicle, and more particularly to an apparatus for steering the front and rear wheels of a straddle-type off-road motor vehicle having wide tires on front and rear wheels.
2. Description of the Relevant Art:
As disclosed in Japanese Laid-Open Patent Publications Nos. 61-232966 (published Oct. 17, 1986) and 61-295174 (published Dec. 25, 1986), there is known an apparatus for steering the front and rear wheels of a straddle-type off-road motor vehicle with wide tires on the front and rear wheels for travelling over rough terrain. The disclosed steering apparatus comprises front and rear wheel steering devices for transmitting steering action of a steering handlebar to the front and rear wheels to steer these wheels. In the steering apparatus disclosed in the former publication, the front wheels are steered in proportion to the turning motion of the steering handlebar, and the rear wheels are progressively steered in the opposite direction to the direction of steering movement of the front wheels. In the steering apparatus disclosed in the latter publication, the front wheels are steered in proportion to the turning motion of the steering handlebar, and the rear wheels are not steered while the steering angle of the steering handlebar is in a relatively small range, but are progressively steered in the opposite direction to the front wheels while the steering angle of the steering handlebar is in a relatively large range.
Since the steering angles of the front and rear wheels are increased as the steering handlebar is turned to a greater extent in both of the disclosed steering apparatus, the steering load applied to the steering handlebar is increased as the turning motion of the steering handlebar is increased. Particularly, the steering load on the steering handlebar becomes maximum when the rear wheels are steered to a maximum angle. More specifically, in the front and rear wheel steering apparatus, inasmuch as the rear wheel steering angle is progressively increased with respect to the steering angle of the steering handlebar, the steering load which the driver applies to the steering handlebar is progressively increased in the vicinity of an angular range where the steering handlebar angle is of a maximum value. In other words, the steering load required for the driver to turn the steering handlebar from a neutral position to a steering limit position (=maximum steering angle position) 25 is smoothly increased at first, but not immediately prior to the steering limit position. Therefore, the conventional front and rear wheel steering apparatus have a tendency for the driver to fail to get a smooth steering feeling at all times during operation of the motor vehicle.